Silicon wafer carrier

ABSTRACT

The present invention relates to a silicon wafer carrier consisting of a composition composed of (a) 100 parts by weight of a polyester, (b) 5 to 100 parts by weight of a polyether ester amide, (c) 10 to 2,500 ppm (based on the polyether ester amide) of an alkaline metal and (d) 0 to 40 parts by weight of a modified polyolefin, generating not more than 10 ppm of volatile gas by the heat-treatment at 150° C. for 60 minutes and eluting not more than 10 ppm of the alkaline metal by the immersion treatment in pure water at 80° C. for 120 minutes. The silicon wafer carrier has the generation of volatile gas and the elution of metal suppressed to an extent not to essentially cause the surface contamination of a silicon wafer and is provided with excellent permanent antistaticity and high mechanical properties and heat-resistance.

This application is a divisional of application Ser. No. 09/147,268filed Nov. 17, 1998, now U.S. Pat. No. 6,268,030 which is a 371 ofPCT/JP97/01171 filed Apr. 4, 1997.

DESCRIPTION

1. Technical Field

The present invention relates to a silicon wafer carrier and itsproduction process, more particularly, to a silicon wafer carrier havinglittle surface-staining tendency and permanent antistaticity and itsproduction process.

2. Background Arts

Polyesters are widely used owing to their excellent moldability,mechanical properties, heat-resistance, chemical resistance, creepresistance, impact resistance, rigidity, etc. Silicon wafers composed ofpolytetramethylene terephthalate (which may be abbreviated hereafter asPBT) are already in use.

Polyester is easily electrified by rubbing, peeling, etc. Varioustroubles may take place by the static charge accumulated on a moldedarticle by electrification. For example, accumulated static charge maycause the generation of electric shock in use and the deposition of duston the surface of the article.

It is known that a polyester can be imparted with antistaticity by theaddition of an antistatic agent.

The antistatic treatment by the addition of an antistatic agent can becarried out by coating or internal addition. The coating processnecessitates an additional step and, accordingly, the internal additionis preferable from the view point of production process.

Kneading of a low-molecular ionic surfactant such as an alkylsulfonicacid salt or an alkylbenzenesulfonic acid salt into a polymer is knownas an internal addition process. A process to use a phosphonium salt isdisclosed in the JP-A 62-230835 (hereunder, JP-A means “JapaneseUnexamined Patent Publication”).

Although high initial antistatic effect can be attained by the methodusing a low-molecular ionic surfactant because of the bleeding of thesurfactant on the surface of the molded article, the process has aproblem of losing the antistatic effect by the wiping or washing of thearticle.

A silicon wafer carrier composed of polytetramethylene terephthalate andcarbon fiber is disclosed in the JP-A 8-88266 as a silicon wafer carrierhaving antistaticity, describing that the silicon wafer carrier hasstatic charge dissipating property, i.e. antistaticity and gives littlegeneration of particulate contaminant caused by friction.

A silicon wafer carrier is used after various treating procedurescomprising an annealing step to remove the strain of the silicon wafercarrier, a degassing step to remove the residual volatile components, awashing step to remove attached contaminant and a subsequent dryingstep.

The silicon wafer carrier is used for the transportation and storage ofa silicon wafer in the heat-treating step and the washing step of thesilicon wafer under various conditions.

A polyether ester amide is known to have good antistaticity, however,the use of the polymer together with other thermoplastic resin causeslaminar peeling and the production of a molded article having desirablemechanical properties is difficult.

A polyester composition composed of a polyester, a polyether ester amideand a modified vinyl polymer is disclosed in the JP-A 9-12844 as acomposition having excellent impact resistance.

DISCLOSURE OF THE INVENTION

A large amount of volatile gases composed of organic gases are generatedduring the transportation and storage of a silicon wafer in the case ofusing a silicon wafer carrier made of conventional polytetramethyleneterephthalate (which may be abbreviated as PBT hereafter) resin for thetransportation and storage of a silicon wafer, and the generated gasesare condensed on the silicon wafer to cause the contamination of thesurface of the wafer. In such a case, the surface contamination of thesilicon wafer takes place by the transfer of an impurity from thesurface of the silicon wafer carrier to the silicon wafer.

Further, metals are dissolved from the silicon wafer carrier in thewashing of the silicon wafer and attached to the surface of the siliconwafer to effect the contamination of the silicon wafer surface.

Such contamination causes the defects and the lowering of electricalproperties of a semiconductor device using the silicon wafer and gives asilicon wafer having qualities unsuitable for use.

The use of a compatibilizing agent for imparting a silicon wafer carrierwith antistaticity improves the compatibility problem, however, theimpurity content in the resin composition increases by the addition of alarge amount of the compatibilizing agent to cause the problem ofsurface contamination, etc., in the case of using the resin as a siliconwafer carrier.

An object of the present invention is to provide a silicon wafer carrierhaving suppressed bleeding tendency of impurities, especially alkalimetals, to the surface of the silicon wafer carrier in heat-treatment toa level not to cause the trouble of the surface contamination of asilicon wafer and, furthermore, having excellent permanentantistaticity.

Another object of the present invention is to provide a silicon wafercarrier having an impurity bleeding tendency suppressed to an extent notto cause the trouble of the surface contamination of a silicon wafer andexhibiting excellent permanent antistaticity, wherein said permanentantistaticity is characterized by the surface resistivity of 1×10¹⁴ to1×10¹¹Ω/□ (measuring voltage: 500V).

Another object of the present invention is to provide a silicon wafercarrier having especially low bleeding of impurities and generation ofvolatile gases.

Another object of the present invention is to provide a silicon wafercarrier having hydrolysis resistance as well as the abovecharacteristics.

Another object of the present invention is to provide a process forproducing the silicon wafer carrier having the above properties.

Another object of the present invention is to provide a process forproducing the silicon wafer carrier while suppressing the Barus effectoccurring in the case of kneading a polyether ester amide with apolyester in molten state and improving the productivity of a siliconwafer carrier compounded with a large amount of a polyether ester amide.

The other object and advantage of the present invention will beclarified by the following explanations.

The present invention comprises the following constitution.

1. A silicon wafer carrier consisting of a composition composed of (a)100 parts by weight of a polyester, (b) 5 to 100 parts by weight of apolyether ester amide, (c) 10 to 2,500 ppm (based on the polyether esteramide) of an alkaline metal and (d) 0 to 40 parts by weight of amodified polyolefin, generating not more than 10 ppm of volatile gas bythe heat-treatment at 150° C. for 60 minutes, and eluting not more than10 ppm of the alkaline metal by the immersion in pure water at 80° C.for 120 minutes:

2. A silicon wafer carrier consisting of a composition composed of (a)100 parts by weight of a polyester, (b) 5 to 30 parts by weight of apolyether ester amide and (c) 10 to 2,500 ppm (based on the polyetherester amide) of an alkaline metal, containing a polyether ester amidephase having an aspect ratio of 3 or more, a minor diameter of 1 μm orless and a major diameter of 1 μm or more in a polyester phase in therange from the surface of the silicon wafer carrier to the depth of 20μm, generating not more than 10 ppm of volatile gas by theheat-treatment at 150° C. for 60 minutes, and eluting not more than 10ppm of the alkaline metal by the immersion in pure water at 80° C. for120 minutes:

3. A silicon wafer carrier consisting of a composition composed of (a)100 parts by weight of a polyester, (b) 31 to 100 parts by weight of apolyether ester amide, (c) 10 to 2,500 ppm (based on the polyether esteramide) of an alkaline metal and (d) 1 to 40 parts by weight of amodified polyolefin, containing a polyether ester amide phase having anaspect ratio of 3 or more, a minor diameter of 1 μm or less and a majordiameter of 1 μm or more in a polyester phase in the range from thesurface of the silicon wafer carrier to the depth of 20 μm, generatingnot more than 10 ppm of volatile gas by the heat-treatment at 150° C.for 60 minutes, and eluting not more than 10 ppm of the alkaline metalby the immersion in pure water at 80° C. for 120 minutes:

4. A silicon wafer carrier consisting exclusively of apolytetramethylene terephthalate, generating not more than 10 ppm ofvolatile gas by the heat-treatment at 150° C. for 60 minutes, andeluting not more than 50 ppb of the alkaline metal by the immersion inpure water at 80° C. for 120 minutes: and

5. A process for producing a silicon wafer carrier described in the item1, characterized by molding (a) a polyester having an intrinsicviscosity of from 0.6 to 1.2 and (b) a polyether ester amide having amelt viscosity of 10 to 1,000 Pa.S measured at 260° C. and a shear rateof 1,000 sec⁻¹ under a molding condition while keeping the meltviscosity ratio of the polyether ester amide (b) to the polyester (a)between 0.01 and 1.

The present invention is described in details as follows.

<<Polyester>>

The polyester of the component (a) to be used in the present inventionis an aromatic polyester produced by using terephthalic acid or2,6-naphthalenedicarboxylic acid as an acid component and an aliphaticdiol such as ethylene glycol, trimethylene glycol, tetramethyleneglycol, hexamethylene glycol and neopentyl glycol as a diol component.

The polyester (a) may be copolymerized with not more than 30 mol %,preferably not more than 20 mol %, more preferably not more than 10 mol% of a copolymerization component based on the total carboxylic acidcomponent.

The polyester (a) is preferably polytetramethylene tere-phthalate,polypropylene terephthalate, polyethylene terephthalate orpolytetramethylene 2,6-naphthalate, especially preferablypolytetramethylene terephthalate having high crystallization rate.

The polyester (a) may be a copolymerized polyester produced bysubstituting a part of the above polyester with a copolymerizationcomponent.

Examples of the acid components of such copolymerization component areisophthalic acid, phthalic acid; alkyl-substituted phthalic acids suchas methylterephthalic acid and methylisophthalic acid;naphthalenedicarboxylic acids such as 2,6-naphthalenedicarboxylic acid,2,7-naphthalenedicarboxylic acid and 1,5-naphthalenedicarboxylic acid;diphenyldicarboxylic acids such as 4,4′-diphenyldicarboxylic acid and3,4′-diphenyldicarboxylic acid; aromatic dicarboxylic acids such as4,4′-diphenoxyethane dicarboxylic acid and diphenoxyethane dicarboxylicacid; aliphatic or alicyclic dicarboxylic acids such as succinic acid,adipic acid, sebacic acid, azelaic acid, decanedicarboxylic acid andcyclohexanedicarboxylic acid; and oxycarboxylic acids such asε-oxycapronic acid, hydroxybenzoic acid and hydroxyethoxybenzoic acid.

Examples of the diol components of such copolymerization component arealicyclic diols such as 1,4-cyclohexanedimethanol; dihydroxybenzenessuch as hydroquinone and resorcinol; bisphenols such as2,2-bis(4-hydroxyphenyl)-propane and bis(4-hydroxyphenyl)-sulfone; andaromatic diols such as ether diol derived from a bisphenol and a glycolsuch as ethylene glycol.

The polyester (a) may contain not more than 1.0 mol %, preferably notmore than 0.5 mol %, more preferably not more than 0.3 mol % of abranching component as the copolymerization component.

Examples of such branching component are polyfunctional ester-formingacids such as trimesic acid and trimellitic acid; and polyfunctionalester-forming alcohols such as glycerol, trimethylolpropane andpentaerythritol.

The polyester used in the present invention preferably has an intrinsicviscosity of from 0.6 to 1.20. A polyester having the intrinsicviscosity falling within the above range has a flowability sufficientfor molding and gives a molded silicon wafer carrier having highrigidity. A large-sized carrier, e.g. a carrier for a wafer of 12 inchin diameter can be produced without generating short-shot. The intrinsicviscosity is a calculated value based on the value measured ino-chlorophenol at 35° C.

The polyester used in the present invention has a terminal carboxylconcentration of preferably 10 equivalent/ton or less, more preferably 5equivalent/ton or less when the polyester is not used in combinationwith a polyether ester amide. The unit “ton” means 10⁶ g. When theterminal carboxyl concentration is within the above range, the obtainedsilicon wafer carrier has sufficiently low generation of volatile gas inheat-treatment and excellent hydrolysis resistance.

The concentration of the terminal carboxyl group (COOH) is the number ofequivalent per 10⁶ g of polymer measured by the A. Conix method[Makromol. Chem. 26, 226(1958)].

The polyester to be used in the present invention is preferably producedby a solid phase polymerization of one or more steps.

The polyester to be used in the present invention can be produced bycarrying out the liquid-phase polycondensation of a dicarboxylic acidcomposed mainly of terephthalic acid or its ester-forming derivativewith a dihydroxy compound composed mainly of tetramethylene glycol orits ester-forming derivative in the presence of a catalyst, pelletizingthe product and subjecting the pellet to solid-phase polycondensationreaction in nitrogen atmosphere at 180 to 225° C. under normal pressurefor 2 to 24 hours.

<<Polyether ester amide>>

The polyether ester amide of the component (b) to be used in the presentinvention is the one derived from (b1) a polyamide having carboxylgroups at both terminals and (b2) an alkylene oxide adduct of abisphenol.

The polyamide (b1) constituting the polyether ester amide (b) of thepresent invention and having carboxyl groups at both terminals is (1) aring-opened lactam polymer, (2) a polycondensation product of anaminocarboxylic acid or (3) a polycondensation product of a dicarboxylicacid and a diamine. Examples of the lactam of the polymer (1) arecaprolactam, enantholactam, laurolactam and undecanolactam; the examplesof the aminocarboxylic acid of the polymer (2) is ω-aminocaproic acid,ω-aminoenanthic acid, ω-aminocaprylic acid, ω-aminopelargonic acid,ω-aminocapric acid, 11-aminoundecanoic acid and 12-aminododecanoic acid;examples of the dicarboxylic acid of the polymer (3) are adipic acid,azelaic acid, sebacic acid, undecane diacid, dodecane diacid andisophthalic acid; and the examples of the diamine arehexamethylenediamine, heptamethylenediamine, octamethylenediamine anddecamethylene-diamine. Two or more kinds of the above exemplifiedamide-forming monomers may be used in combination. Preferable monomersamong the above examples are caprolactam, 12-aminododecanoic acid andadipic acid-hexamethylenediamine, especially preferably caprolactam.

The polyamide (b1) can be produced by the ring-opening polymerization orpolycondensation of the above amide-forming monomer by conventionalmethod in the presence of a dicarboxylic acid component having a carbonnumber of from 4 to 20 as a molecular weight controlling agent. Examplesof the dicarboxylic acid having a carbon number of from 4 to 20 arealiphatic dicarboxylic acids such as succinic acid, glutaric acid,adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid,undecane diacid and dodecane diacid; aromatic dicarboxylic acids such asterephthalic acid, isophthalic acid, phthalic acid andnaphthalenedicarboxylic acid; alicyclic dicarboxylic acids such as1,4-cyclohexanedicarboxylic acid and dicyclohexyl-4,4′-dicarboxylicacid; and alkaline metal salts of 3-sulfoisophthalic acid such as sodium3-sulfoisophthalate and potassium 3-sulfoisophthalate. Preferable acidsamong the above examples are aliphatic dicarboxylic acids, aromaticdicarboxylic acids and alkaline metal salts of 3-sulfoisophthalic acid,and especially preferable acids are adipic acid, sebacic acid,terephthalic acid, isophthalic acid and sodium 3-sulfoisophthalate.

The number-average molecular weight of the polyamide (b1) is 500 to5,000, preferably 500 to 3,000. When the number-average molecular weightof the polyamide (b1) is smaller than 500, the heat-resistance of thepolyether ester amide is lowered, and if it exceeds 5,000, thereactivity is lowered to necessitate a long time for the production ofthe polyether ester amide.

Examples of the bisphenols of the alkylene oxide adduct of a bisphenol(b2) which is another component constituting the polymer (b) arebisphenol A (4,4′-dihydroxydiphenyl-2,2-propane), bisphenol F(4,4′-dihydroxydiphenylmethane), bisphenol S(4,4′-dihydroxydiphenylsulfone) and 4,4′-dihydroxydiphenyl-2,2-butane;and especially preferable compound among the above examples is bisphenolA. The alkylene oxides of the adduct (b2) are ethylene oxide, propyleneoxide, 1,2- or 1,4-butylene oxide or a mixture of two or more of theabove compounds. Ethylene oxide is preferable among the above examples.

The number-average molecular weight of the ethylene oxide adduct (b2) ofbisphenol is usually 300 to 5,000, preferably 1,000 to 3,000, especiallypreferably 1,600 to 3,000. More preferably, the adduct has an ethyleneoxide molar number of 30 to 60. When the number-average molecular weightis smaller than 300, the antistaticity becomes insufficient, and if itexceeds 5,000, the reactivity is lowered to necessitate a long time forthe production of the polyether ester amide.

The polyether ester amide to be used in the present invention as thecomponent (b) is preferably a polyether ester amide derived from apolyamide having carboxyl groups on both terminals and a polyethercomponent consisting of an ethylene oxide adduct of a bisphenol havinghigh molecular weight, especially preferably a polyether ester amidederived from an ethylene oxide adduct of bisphenol having an ethyleneoxide molar number of 30 to 60.

The amount of the alkylene oxide adduct (b2) in the component (b) ispreferably 20 to 80% by weight, especially preferably 25 to 75% byweight based on the sum of (b1) and (b2). When the amount of (b2) issmaller than 20% by weight, the antistaticity of the component (b) isdeteriorated, and when it exceeds 80% by weight, the heat-resistance ofthe component (b) is lowered to an undesirable level.

There is no particular restriction on the process for the production ofthe component (b), and the following processes {circle around (1)} and{circle around (2)} can be shown as examples.

Process {circle around (1)}: An amide-forming monomer is made to reactwith a dicarboxylic acid to form a polyamide (b1), an alkylene oxideadduct (b2) is added thereto and the components are polymerized at hightemperature under reduced pressure.

Process {circle around (2)}: An amide-forming monomer, a dicarboxylicacid and the component (b2) are charged into a reactor at the same time,the components are reacted with each other at a high temperature underpressure in the presence or absence of water to produce a polyamide (b1)as an intermediate and the polymerization reaction of (b1) with (b2) iscarried out under reduced pressure.

The above polymerization reaction is carried out usually by using aconventional esterification catalyst. Examples of the catalyst areantimony-based catalysts such as antimony trioxide, tin-based catalystssuch as monobutyltin oxide, titanium-based catalysts such as tetrabutyltitanate, zirconium-based catalysts such as tetrabutyl zirconate, andmetal acetate-based catalysts such as zinc acetate. The amount of thecatalyst is usually 0.1 to 5% by weight based on the sum of (b1) and(b2).

The polyether ester amide (b) to be used in the present invention has amelt viscosity of 10 to 1,000 Pa.S measured at 260° C. under a shearingrate of 1,000 sec⁻¹, and the melt viscosity ratio of the polyether esteramide (b) to the polyester under the above condition is preferablybetween 0.01 and 1.

The melt viscosity ratio of a polyester and a polyether ester amide ispreferably between 0.01 and 1, more preferably between 0.1 and 1 fordeveloping various characteristics such as permanent antistaticity bythe melt-mixing of a polyester and a polyether ester amide havingessentially low compatibility and different melt viscositycharacteristics. The fine dispersion of the polyether ester amidebecomes difficult and the development of antistatic effect is scarcelyattainable when the ratio is larger than 1 or smaller than 0.01.

It is surprising that a polyether ester amide (b) having a meltviscosity of 10 to 1,000 (Pa.S) at 260° C. under a shearing rate of1,000 sec⁻¹ and a melt viscosity ratio to the polyester (a) of between0.01 and 1 can be dispersed in a polyester matrix in a desirable stateand the molten mixture exhibits high fluidity in injection moldingsubjected to high shearing stress. Further surprising fact is that thepolyether ester amide is deviated to the surface layer in the fillingstage of the resin in a mold to obtain a silicon wafer carrierdeveloping excellent permanent antistaticity in high reproducibility inthe case of an injection molding of a silicon wafer carrier with a resincomposed of a polyester and a polyether ester amide having meltviscosity values satisfying the above condition.

The amount of the polyether ester amide (b) in the present invention is5 to 100 parts by weight based on 100 parts by weight of the polyester(a). When the composition is free from modified polyolefin (c), thecompounding amount of the polyether ester amide (b) is preferably 5 to30 parts by weight, more preferably 10 to 20 parts by weight based on100 parts by weight of the polyester (a). In the case that thecomposition contains the modified polyolefin (c), the amount of thepolyether ester amide (b) is preferably 31 to 100 parts by weight basedon 100 parts by weight of the polyester (a).

A sufficient permanent antistaticity cannot be imparted when the amountof the polyether ester amide is smaller than the lower limit of theabove range and the mechanical strength and productivity are lowered toundesirable levels when the amount is larger than the above range.

<<Alkaline metal>>

The alkaline metal (c) in the present invention is an element belongingto the group Ia alkali metal or group IIa alkaline earth metal of theperiodic table; concretely, lithium, sodium, potassium, rubidium,cesium, francium, beryllium, magnesium, calcium, strontium, barium orradium. These elements may be used in combination. The alkaline metal ispreferably present in the composition by adding the metal in the form ofan alkaline metal compound.

Examples of the alkaline metal compound are hydroxide, inorganic acidsalt and organic acid salt such as acetate, carbonate and ammonium salt.These compounds may be used in combination. Concrete examples of thecompound are lithium hydroxide, sodium hydroxide, potassium hydroxide,rubidium hydroxide, cesium hydroxide, francium hydroxide, berylliumhydroxide, magnesium hydroxide, calcium hydroxide, strontium hydroxide,barium hydroxide, radium hydroxide; lithium acetate, sodium acetate,potassium acetate, magnesium acetate, calcium acetate; lithiumcarbonate, sodium carbonate, and potassium carbonate.

The compounding amount of the alkaline metal (c) is preferably 10 to2,500 ppm, more preferably 200 to 2,500 ppm based on the polyether esteramide. The antistatic effect is insufficient when the amount is lessthan 10 ppm, and the amount of alkaline metal eluted in the use of asilicon wafer carrier increases to fail in the use of the resin as asilicon wafer carrier when the compounding amount exceeds 2,500 ppm.

<<Modified polyolefin>>

The modified polyolefin (d) in the present invention is a copolymerproduced by the copolymerization of an unsaturated epoxy compound (d1)and one or more kinds of ethylenic unsaturated compounds (d2).

The modified polyolefin (d) contains the unsaturated epoxy compound (d1)as a copolymerization component in an amount of 0.1 to 50% by weight,preferably 1 to 30% by weight.

The unsaturated epoxy compound (d1) is a compound having an epoxy groupand an unsaturated group copolymerizable with an ethylenic unsaturatedcompound in the molecule; for example, an unsaturated glycidyl ester andan unsaturated glycidyl ether expressed by the following generalformulas (1) and (2), respectively.

in the above general formula (1), R is a hydrocarbon group having acarbon number of from 2 to 18 and containing an ethylenic unsaturatedbond.

in the above general formula (2), R is a hydrocarbon group having acarbon number of from 2 to 18 and containing an ethylenic unsaturatedbond, and X is —CH₂—O— or

Concrete examples of the unsaturated epoxy compound (d1) are glycidylacrylate, glycidyl methacrylate, itaconic acid glycidyl ester, allylglycidyl ether, 2-methylallyl glycidyl ether and styrene-p-glycidylether.

The ethylenic unsaturated compound (d2) is, for example, olefins, vinylesters of a saturated carboxylic acid having a carbon number of from 2to 6, esters of a saturated alcohol component having a carbon number offrom 1 to 8 and an acid, vinyl halides, styrenes, nitriles, vinyl ethersand acrylamides. The acid of the ester of a saturated alcohol having acarbon number of from 1 to 8 and an acid is, for example, acrylic acid,methacrylic acid, maleic acid, and fumaric acid.

Concrete examples of the ethylenic unsaturated compound (d2) areethylene, propylene, 1-butene, vinyl acetate, methyl acrylate, ethylacrylate, methyl methacrylate, diethyl maleate, diethyl fumarate, vinylchloride, vinylidene chloride, styrene, acrylonitrile, isobutyl vinylether and acrylamide, preferably ethylene, vinyl acetate and methylacrylate.

The modified polyolefin can be produced by various methods including arandom copolymerization to introduce an unsaturated epoxy compound intothe main chain of a copolymer and a graft copolymerization to introducean unsaturated epoxy compound as a side chain of a copolymer.

The amount of the modified polyolefin used as the component (d) in thepresent invention is preferably 1 to 40 parts by weight, more preferably3 to 10 parts by weight based on 100 parts by weight of the polyester(a). The use of less than 1 part by weight of the modified polyolefingives insufficient effect to suppress the Barus effect in extrusion andimprove the productivity and, on the contrary, a composition containingmore than 40 parts by weight of the modified polyolefin has a mechanicalstrength lowered to an undesirable level.

<<Silicon wafer carrier>>

The silicon wafer carrier of the present invention preferably contains apolyether ester amide phase having an aspect ratio of 3 or above, aminor diameter of 1 μm or less and a major diameter of 1 μm or more in apolyester phase within the range from the surface of the silicon wafercarrier to a depth of 20 μm. The polyether ester amide phase has itsmajor axis directed parallel to the surface of the silicon wafercarrier. Preferably, the polyether ester amide phases are brought intocontact with each other or present close to each other at a distance of0.5 μm or less for getting excellent antistaticity.

Good antistaticity cannot be attained when the aspect ratio of thepolyether ester amide phase is smaller than 3. It is also unattainablewhen the minor diameter of the polyether ester amide phase exceeds 1 μmor the major diameter of the phase is shorter than 1 μm.

The silicon wafer carrier of the present invention has a permanentantistaticity corresponding to a surface resistivity of 1×10¹⁴ to1×10¹¹Ω/□, preferably 1×10¹³ to 1×10¹¹Ω/□, more preferably 1×10¹² to1×10¹¹ Ω/□. An antistaticity sufficient for a silicon wafer carrier canbe attained when the surface resistivity is within the above range.

The amount of volatile gas generated by heating the silicon wafercarrier of the present invention at 150° C. for 60 minutes should be 10ppm or below, preferably 5 ppm or below.

The amount of volatile gas generated from the silicon wafer carrier isdetermined by head-space gas chromatography on 10 grams of a specimenproduced by crushing a silicon wafer carrier to flakes of 5 mm square.

When the generation of volatile gas exceeds 10 ppm, the surfacecontamination of a silicon wafer with the volatile gas deteriorates thequality of the silicon wafer resulting in the defects of electronicdevices such as LSI manufactured by processing the silicon wafer.

The volatile gases generated by the heat-treatment of a silicon wafercarrier are mainly organic gases such as acetaldehyde, acetone,tetrahydrofuran and 3-buten-1-ol. These volatile gases are condensed ona silicon wafer or transferred to a silicon wafer after condensed on thesilicon wafer carrier to cause the contamination of the surface of thesilicon wafer.

The amount of alkaline metal eluted by immersing the silicon wafercarrier of the present invention in pure water at 80° C. for 120 minutesis required to be 10 ppm or below, preferably 50 ppb or below,especially preferably 10 ppb or below.

The amount of alkaline metal eluted from a silicon wafer carrier isdetermined by crushing a silicon wafer carrier to flakes of 5 mm square,immersing 10 g of the obtained specimen in 80 ml of pure water at 80° C.for 120 minutes, and measuring the amount of alkaline metal eluted inthe pure water with an atomic absorption photometer.

When the elution of alkaline metal exceeds 10 ppm, the surfacecontamination of a silicon wafer with the alkaline metal deterioratesthe quality of the silicon wafer resulting in the defects of electronicdevices such as LSI manufactured by processing the silicon wafer.

The elution amount of alkaline metal is 50 ppb or less, preferably 10ppb or less when the silicon wafer carrier is free from antistaticity.When the elution amount of alkaline metal is within the above range,there is essentially no surface contamination of silicon wafer withalkaline metal and the elution does not cause the defect of electronicdevices such as LSI manufactured by processing the silicon wafer.

The surface contamination of a silicon wafer with an alkaline metal iscaused by the deposition of the alkaline metal eluted from a siliconwafer carrier on the silicon wafer mainly in a silicon wafer washingprocess.

When the silicon wafer carrier of the present invention is free frompolyether ester amide, i.e. composed exclusively of polytetramethyleneterephthalate, the generation of volatile gas should be 10 ppm or belowand the elution of alkaline metal should be 50 ppb or below. It is shownbefore that these conditions are necessary to be satisfied for a siliconwafer carrier crushed to flakes of 5 mm square, and such a silicon wafercarrier can be produced by molding polyester pellets generating not morethan 10 ppm, preferably not more than 5 ppm of volatile gas in the caseof heat-treatment at 150° C. for 60 minutes in the form of pellets andeluting not more than 50 ppb, preferably not more than 10 ppb ofalkaline metal in the case of immersing the pellets in pure water at 80°C. for 120 minutes. The amounts of generated volatile gas and elutedalkaline metal of the pellets are measured by the methods similar to themeasurements on the crushed silicon wafer carrier.

<<Additives>>

The resin composition to be used in the present invention may beincorporated, within a range not to deteriorate the object of thepresent invention, with additives such as a fibrous reinforcing agentrepresented by glass fiber, a particulate or flaky filler, aflame-retardant, a mold-releasing agent, a lubricant, a slip agent, anucleating agent, a colorant, an antioxidant, a heat-stabilizer, a light(weather) stabilizer, a thermoplastic resin other than those specifiedas a component of the present resin composition, and a modifier such asan impact modifier.

<<Molding>>

The resin composition to be used in the present invention can beproduced by an arbitrary compounding method. The compounding componentsof the present invention are preferably more effectively dispersed infinely dispersed state, and the total or a part of the components arepreferably mixed with each other simultaneously or separately by a mixersuch as blender, kneader, Banbury mixer, roll mill or extruder and themixture is molded in the form of a silicon wafer carrier.

As an alternative method, a composition dry-blended beforehand ishomogenized by melting and kneading with a heated extruder, extruded inthe form of a thread, cut to desired length and molded in the form of asilicon wafer carrier.

Molding pellets of the resin composition to be used in the presentinvention can be produced by blending, e.g. dry-blending individualcomponents by conventional method, melting and kneading with a ventedtwin-screw extruder having a screw diameter of 44 mm at a cylindertemperature of 200 to 280° C., preferably 220 to 250° C., a screwrotational speed of 160 to 300 rpm, and an extrusion rate of 30 to 60kg/h, cooling the thread extruded through a die and cutting the cooledthread.

The molding of the silicon wafer carrier of the present invention can becarried out by using a general molding machine for thermoplastic resin.The silicon wafer carrier of the present invention can be produced fromthe above pellets by injection molding with an injection molding machineunder an injection pressure of 600 to 1,000 kg/cm² at an injection rateof 60 to 90 cm³/sec.

The ratio of the melt viscosity of the polyether ester amide (b) to themelt viscosity of the polyester (a) is necessary to fall within therange of 0.01 to 1 in the above case. The melt viscosity ratio can beadjusted by controlling the cylinder temperature, the injection rate andthe injection pressure.

The silicon wafer carrier of the present invention is required to bemolded under a higher pressure at a higher speed compared with themolding conditions of conventional polyesters. For example, in the caseof using a Mitsubishi 80MSP Injection Molding Machine, the molding ispreferably carried out at a cylinder temperature of 230 to 260° C., amold temperature of 40 to 80° C., an injection speed of 40 to 60% and aninjection pressure of 40 to 60%. The silicon wafer carrier producedunder the above molding condition has excellent permanent antistaticity.

The molding under the above conditions forms a polyether ester amidephase having an aspect ratio of 3 or above, a minor diameter of 1 μm orless and a major diameter of 1 μm or above in a polyester phase withinthe range from the surface of the silicon wafer carrier to the depth of20 μm, and the obtained silicon wafer carrier has a surface resistivityof 1×10¹⁴ to 1×10¹¹Ω/□, preferably 1×10¹³ to 1×10¹¹Ω/□, more preferably1×10¹² to 1×10¹¹Ω/□.

The silicon wafer carrier of the present invention is imparted withpermanent antistaticity by the segregation of the polyether ester amideto the surface of the silicon wafer carrier, causes extremely lowmigration of metallic impurities to the surface of the silicon wafercarrier by heat-treatment, and does not generate the surfacecontamination of a silicon wafer by the transfer of contaminant from thecarrier.

Such segregation phenomenon and permanent antistaticity are developed inhigh reproducibility in a silicon wafer carrier composed of a polyester,an alkaline metal and a polyether ester amide satisfying the conditionsshown in the present invention. The segregation phenomenon and permanentantistaticity are developed in higher reproducibility in a silicon wafercarrier composed of a polyester, an alkaline metal, a polyether esteramide and a modified polyolefin satisfying the conditions shown in thepresent invention.

EXAMPLE

The present invention is described by the following Examples.

The evaluation of the characteristics were performed by the followingevaluation methods.

(1) Specific surface resistance

Specific surface resistance (surface resistivity) was measured by usinga super-insulation meter (TOA Electronics Ltd.; SM-10E).

Measurement conditions:

Ambient temperature: 23° C.

Relative humidity: 50% RH

Measuring voltage: 500V.

(2) Static charge decay period

Static charge decay period is the half-decay time measured by an honestmeter (Shishido Electrostatic, Ltd.; Static H-0110).

Measurement conditions:

Ambient temperature: 23° C.

Relative humidity: 50% RH

Applied voltage: 10.0 kV.

(3) Extrudability

The aforementioned vented twin-screw extruder having a screw diameter of44 mm (Japan Steel Works, Ltd., TEX44S-30AW-2V) was used and theextrudability of a resin was evaluated by charging 10 kg of the resin tothe extruder.

O: Extrudable in ordinary state.

X: Unable to take-up with a cutter owing to frequent thread breakage.

(4) Amount of eluted alkaline metal

The evaluation of the elution of alkaline metal was performed byimmersing 10 grams of a specimen (a silicon wafer carrier crushed toflakes of 5 mm square) in 80 ml of pure water at 80° C. for 120 minutesand determining the amount of eluted alkaline metal in pure water withan atomic absorption photometer (Hitachi Ltd.; Z8100) after theimmersion treatment.

(5) Amount of generated volatile gas

The evaluation of the amount of generated volatile gas was carried outby heating 10 grams of a specimen (a silicon wafer carrier crushed toflakes of 5 mm square) at 150° C. for 60 minutes and determining theamount of generated volatile gas by gas chromatography.

The gas chromatography was performed by using a head-space gaschromatography (Shimadzu Corp.: HS-GC: GC-9A HSS-2A and CR-4A).

The conditions of analysis are shown below.

1) Column

Silicon 0V-1701, Id 0.25 mm×50 mm, df 0.3 μm

2) Carrier gas: He 1.5 kg/cm²G

3) Split ratio: Split/column=60/0.75=80

4) Septum purge flow rate: 1.5 ml/min

5) Column INI. Temp: 50° C.

6) Column INI. Time: 2 min

7) Column P. RATE: 10° C./min

8) Column FINE. Temp: 250° C.

9) Column FINE. Time: 10 min

10)INI. Temp: 300° C.

11)DET. RANGE: 10×1

12)CR-4A WIDTH: 5 sec

13)ATTEN: 2

14)MIN. AREA: 100

15)STOP. TM: 33 min

16)SPEED: 10 mm/min

(6) Amount of alkaline metal element in silicon wafer carrier

The evaluation of the amount of the alkaline metal elements in a siliconwafer carrier was carried out by decomposing 200 mg of a specimen (asilicon wafer carrier crushed to flakes of 5 mm square) in wet state,and determining the alkaline metal by ICP analysis using JY1700L TRACE(Rigaku Inc.).

(7) Tensile strength

The tensile strength was measured in conformity to ASTM D638.

(8) Heat-deformation temperature

Heat-deformation temperature was determined by measuring deflectiontemperature under load in conformity to ASTM D648 (4.6 kg/cm²).

(9) Polymerization of PBT (QK)

The polytetramethylene terephthalate (QK) used in the Examples wasprepared by the following method.

Dimethyl terephthalate (3,500 parts), butanediol (2,560 parts), andtitanium tetrabutoxide (26 parts) were charged in a reactor andsubjected to transesterification reaction.

The components were transferred to a polymerization reactor when theamount of distilled out methanol reached about 85% of the theoreticalvalue, the pressure was gradually lowered and the polymerizationreaction was performed at 246° C. under reduced pressure. After thereaction, the content of the reactor was discharged, cooled andpelletized. The pellets had an intrinsic viscosity of 0.69. The pelletswere crystallized and subjected to solid-phase polymerization at 190° C.The obtained pellets had an intrinsic viscosity of 0.92 and a terminalcarboxyl group content of 3.5 equivalent/ton.

(10)Raw materials

Various resins and alkaline metal compound used in the Examples are asfollows.

PBT (QK)

Polytetramethylene terephthalate (QK) produced by the above method.

Polyether ester amide (which may be abbreviated as PEEA hereafter)

Pelestat 6321, product of Sanyo Chemical Industries Ltd.

Alkaline metal compound

Potassium chloride, product of Wako Pure Chemical Industries, Ltd.

Glycidyl-modified polyolefin acrylic acid ester

BF-7M, product of Sumitomo Chemical Co., Ltd.

A copolymer composed of 64% by weight of ethylene, 6% by weight ofglycidyl methacrylate and 30% by weight of methyl acrylate as monomercomponents.

PBT

Product of TEIJIN Ltd.; commercial name: C7000

terminal carboxyl group concentration: 47 equivalent/ton

intrinsic viscosity: 1.07

PBT

PBT produced by solution polymerization

product of TEIJIN Ltd., commercial name: TRB-J

terminal carboxyl group concentration: 52 equivalent/ton

PBT

PBT produced by solution polymerization

product of TEIJIN Ltd., commercial name: TRB-K

terminal carboxyl group concentration: 42 equivalent/ton

Polypropylene (PP)

Product of Mitsui Toatsu Chemicals Inc.,

commercial name: BJS-G

Examples 1 to 12

<<Molding of silicon wafer carrier and preparation of test pieces(composition)>>

A PBT composition containing a polyether ester amide and a modifiedpolyolefin was used in the above examples, and a silicon wafer carrierwas molded by the following method.

The raw materials described in the Table 1 were homogeneouslydry-blended beforehand at ratios described in the Table 1, and kneadedin molten state with a vented twin-screw extruder having a screwdiameter of 44 mm at a cylinder temperature of 180 to 310° C., a screwrotation speed of 160 rpm and an extrusion rate of 40 kg/h. The threadextruded through a die was cooled and cut to obtain pellets for molding.

The pellets were injection-molded under an injection pressure of 750kg/cm² at an injection rate of 70 cm³/sec, a cooling time of 15 sec anda total cycle time of 25 sec to obtain a silicon wafer carrier. Testpieces were prepared by cutting the side face of the carrier toprescribed sizes.

The melt viscosity of the polyether ester amide in the molding of thesilicon wafer carrier was 65 (Pa.S) at 260° C. and a shearing rate of1,000 sec⁻¹. The ratio of the melt viscosity of the polyether esteramide to that of the polyester was 0.65 (shearing rate: 1,000 sec⁻¹) andthe cylinder temperature was 250° C.

The melt viscosity ratio in the Table 2 is defined by the followingformula.

(Melt viscosity ratio)=(Melt viscosity of PEEA)/(Melt viscosity of PBT)

The measurement of the melt viscosity was carried out at 250° C. and ashearing rate of 1,000 sec⁻¹.

Example 1

A silicon wafer carrier was molded by the above molding method. Theextrudability was good.

A test piece was prepared according to the above method and subjected tothe above evaluations. The silicon wafer carrier showed an antistaticitycorresponding to the surface resistivity of 10¹²Ω/□ or below, which is alevel unattainable by conventional methods. The results are shown in theTable 1 and the Table 2.

TABLE 1 PBT(QK) PEEA BF-7M (wt. %) (wt %) (wt %) Extrudability Example 172 25 3 ◯ Example 2 66.5 27.5 6 ◯ Example 3 64 30 6 ◯ Example 4 85 15 0◯ Example 5 82 18 0 ◯ Example 6 75 25 0 X Example 7 72.5 27.5 0 XExample 8 70 30 0 X Example 9 100 0 0 ◯

TABLE 2 Half decay Melt PEE BF- Surface time of vis- PBT(QK) A 7Mresistivity static cosity (wt %) (wt %) (wt %) (Ω/□) charge (sec) ratioExam- 72 25 3 4.0E + 11 0.5 0.65 ple 1 Exam- 66.5 27.5 6 2.0E + 11 0.50.65 ple 2 Exam- 64 30 6 1.0E + 11 0.5 0.65 ple 3 Exam- 85 15 0 4.0E +12 1.5 0.65 ple 4 Exam- 82 18 0 2.0E + 12 0.8 0.65 ple 5 Exam- 100 0 0 ≧≧300 — ple 9 1.0E + 15

Examples 2 and 3

Silicon wafer carriers were molded, and test pieces were prepared andevaluated similar to the Example 1.

The results are shown in the Table 1 and the Table 2.

Examples 4 and 5

Silicon wafer carriers were molded, and test pieces were prepared andevaluated similar to the Example 1. The results are shown in the Table 1and the Table 2.

These are examples containing 18 to 15% by weight of the polyether esteramide, and the surface resistivity values were 1×10¹³Ω/□ or below.

Examples 6 to 8

These are examples characterized simply by the increased content ofpolyether ester amide. The take-up of thread was extremely difficult inthe extrusion of the molten resin through a die of the twin-screwextruder owing to Barus effect failing in getting resin pellets.

Example 9

A silicon wafer carriers was molded, and test pieces were prepared andevaluated similar to the Example 1. The results are shown in the Table 1and the Table 2. The example is characterized by the exclusive use ofPBT, and the resin was extrudable similar to ordinary resins.

Examples 10 to 12

Silicon wafer carriers were molded, and test pieces were prepared andevaluated similar to the Example 1. The results are shown in the Table3.

TABLE 3 PBT (QK) PEEA BF-7M Amount of eluted (wt %) (wt %) (wt %)alkaline metal (ppm) Example 10 72 25 3 <4 Example 11 66.5 27.5 6 <4Example 12 85 15 0 <4

The amount of eluted alkaline metal in a system added with a polyetherester amide and a modified polyolefin was comparable to the amount inthe Example containing 15% by weight of a polyether ester amide.

Examples 13 to 16

<<Molding of silicon wafer carrier 2 (composition)>>

PBT compositions containing a polyether ester amide were used in theseExamples, and silicon wafer carriers were molded by the followingmethod. The test pieces were prepared by the following method.

A polyether ester amide was compounded to a PBT (QK) at ratios shown inthe Table 2-1. The components were mixed with each other and kneaded inmolten state with an extruder at 260° C., a screw rotational speed of240 rpm and an extrusion rate of 50 kg/h. The thread extruded throughthe die was cooled and cut to obtain pellets for molding. Silicon wafercarriers were molded by the injection molding of the pellets under aninjection pressure of 750 kg/cm² at an injection rate of 68 cm³/sec.

Separately, test pieces were produced by the injection molding of thepellets under an injection pressure of 750 kg/cm², an injection rate of70 cm³/sec, a cooling time of 15 sec and a total molding cycle of 25sec.

The melt viscosity ratio in the Table 4 is defined by the followingformula.

(Melt viscosity ratio)=(Melt viscosity of PEEA)/(Melt viscosity of PBT)

The measurement of the melt viscosity was carried out at 260° C. and ashearing rate of 1,000 sec⁻¹.

Example 13

A test piece was prepared by the above method at component ratiosdescribed in the Table 4 and evaluated by the above evaluation methods.The result is shown in the Table 4.

TABLE 4 Half decay Melt PEE Surface time of vis- PBT(QK) A resistivitystatic cosity (wt %) (wt %) (Ω/□) charge (sec) ratio Example 13 85.015.0 2.9E + 12 1.2 0.30 Example 14 82.0 18.0 2.0E + 12 0.8 0.30 Example15 80.0 20.0 1.0E + 12 0.6 0.30 Example 16 100.0   0.0 ≧ 100.0  — 1.0E +15

Examples 14 to 16

Test pieces were prepared by the above method similar to the Example 13at component ratios described in the Table 4 and the above evaluationswere carried out. The results are shown in the Table 4.

Example 17

A silicon wafer was produced according to the above method at componentratios similar to the Example 13. A test piece was prepared by cuttingthe silicon wafer carrier at the part to be brought into contact with asilicon wafer.

The antistaticity of the test piece was evaluated according to the abovemethod, and the half decay time was 3 sec, showing excellent antistaticcharacteristics as a silicon wafer carrier.

The test piece was heat-treated at 160° C. for 5 hours, and theantistaticity was evaluated in the similar manner to get a half decaytime of 2 sec, revealing that excellent antistaticity was maintainedafter the heat-treatment.

The amount of alkali metal eluted from the silicon wafer carrier wasevaluated according to the above method. It was 0.9 ppm, i.e. anextremely low level.

Examples 18 to 22

<<Molding of silicon wafer carrier 3 (simple PBT)>>

Exclusively PBT (QK) was used in the Examples 18 to 22, and the siliconwafer carriers were molded by the following method. The test pieces wereprepared by the following method.

Molding pellets were produced by melting and kneading PBT (QK) with anextruder at 260° C., a screw rotational speed of 160 rpm and anextrusion rate of 50 kg/h, cooling the thread extruded through a die andcutting the cooled thread.

The molding pellets were injection-molded at a cylinder temperature of250° C. and a mold temperature of 60° C. to obtain a silicon wafercarrier of 8 inch size. The silicon wafer carrier was crushed to flakesof 5 mm square to obtain a specimen for the analyses of volatile gas andeluted alkaline metal.

Test pieces were produced from the molding pellets by injection moldingand used for the evaluation of mechanical strength and heat-resistance(deflection temperature under load).

Example 18

A silicon wafer carrier was molded by using PBT (QK) as the PBT.

Specimens for the analyses of volatile gas and eluted alkaline metalwere prepared. The amount of generated volatile gas was 3 ppm, and themain component of the volatile gas was THF. The measured result of theeluted alkaline metal was 2.2 ppb or below. The resin exhibitedextremely low generation of volatile gas as well as elution of alkalinemetal and was excellent as a resin for a silicon wafer carrier.

It had strength and heat-resistance indispensable in a silicon wafermanufacturing process.

The evaluation results are shown in the Table 5.

TABLE 5 Heat Amount of distortion Amount of eluted Tensile temperaturegenerated alkaline Resin strength (4.6 volatile metal (grade) (Mpa)kg/cm²) gas (ppm) (ppb) Example PBT(QK) 54.0 155.0  3.0  2.2 18 ExamplePBT(C7000) 54.0 155.0 300.0 110.0 19 Example PP(BJS-G) 29.0 110.0 500.0100.0 20

Example 19

A silicon wafer carrier was produced and evaluated similar to theExample 18 except for the use of PBT (Teijin Ltd.; C7000) in place ofthe PBT (QK) of the Example 18. The results are shown in the Table 5.

Example 20

A silicon wafer carrier was produced and evaluated similar to theExample 18 except for the use of polypropylene (Mitsui Toatsu ChemicalsInc.; BJS-G) in place of the PBT (QK) of the Example 18. The results areshown in the Table 5.

Example 21

A silicon wafer carrier was produced and evaluated similar to theExample 18 by using PBT (Teijin Ltd.; TRB-J) in place of PBT (QK) of theExample 18. The main component of the volatile gas was THF. The resultsare shown in the Table 6.

Example 22

A silicon wafer carrier was produced and evaluated similar to theExample 18 by using PBT (Teijin Ltd.; TRB-K) in place of PBT (QK) of theExample 18. The main component of the volatile gas was THF. The resultsare shown in the Table 6.

TABLE 6 Amount Amount of of eluted generated alkaline ResinPolymerization volatile metal (grade) process gas (ppm) (ppb) ExamplePBT(QK) Solid-phase polymer-  3.0 2.2 18 ization after solutionpolymerization Example PBT(TRB- Solution 21.0 0.0 21 J) polymerizationExample PBT(TRB- Solution 37.4 0.0 22 K) polymerization

Example 23

The amounts of alkaline metal elements existing in the silicon wafercarriers of the Examples 1 to 16 were measured. The results are shown inthe Table 7.

TABLE 7 Amount of alkaline BF- metal in Ratio of PBT(QK) PEEA 7M siliconwafer alkaline metal (wt %) (wt %) (wt %) carrier (ppm) to PEEA (ppm)Example 72 25 3 249 996 1 Example   66.5   27.5 6 248 902 2 Example 6430 6 282 940 3 Example 85 15 0 132 880 4 Example 82 18 0 166 922 5Example 75 25 0 233 932 6 Example   72.5   27.5 0 260 945 7 Example 7030 0 297 990 8 Example 100   0 0  0  0 9 Example 85 15 0 134 893 13Example 82 18 0 162 900 14 Example 80 20 0 190 950 15 Example 100   0 0 0  0 16

Examples 24 to 28

The following 5 kinds of PEEA were prepared by adjusting the amount ofalkaline metal in PEEA with potassium chloride.

PEEA<10: PEEA having an alkaline metal content of less than 10 ppm basedon PEEA

PEEA120: PEEA having an alkaline metal content of 120 ppm based on PEEA

PEEA900: PEEA having an alkaline metal content of 900 ppm based on PEEA

PEEA2000: PEEA having an alkaline metal content of 2,000 ppm based onPEEA

PEEA3000: PEEA having an alkaline metal content of 3,000 ppm based onPEEA

Example 24

A test piece was prepared similar to the Example 13 by using a resincomposition containing the above PEEA resins at ratios shown in theTable 8. The units of PBT and PEEA in the Table are wt %.

The Example 24 is a case having an alkaline metal content of less than10 ppm relative to PEEA, and sufficient antistatic performance wasunattainable in this case.

TABLE 8 Amount PEE PEE PEE PEE PEE of PBT A A A A A eluted (QK) <10 120900 2000 3000 Surface alkaline (wt (wt (wt (wt (wt (wt resistiv- metal%) %) %) %) %) %) ity(Ω) (ppm) Exam- 85 15 — — — — 2.0E + 14 <4 ple 24Exam- 85 — 15 — — — 2.3E + 13 <4 ple 25 Exam- 85 — — 15 — — 1.2E + 12 <4ple 26 Exam- 85 — — — 15 — 1.4E + 12 <4 ple 27 Exam- 85 — — — — 151.1E + 12 >10 ple 28

Example 25

A test piece was produced similar to the Example 24.

The amount of eluted metal was small and the test piece exhibitedsufficient antistaticity.

Example 26

A test piece was produced similar to the Example 24.

The amount of eluted metal was small and the test piece exhibitedsufficient antistaticity.

Example 27

A test piece was produced similar to the Example 24. The amount ofeluted metal was small and the test piece exhibited sufficientantistaticity.

Example 28

A test piece was produced similar to the Example 24.

The content of alkaline metal was 3,000 ppm based on PEEA in the Example28, and the amount of eluted metal was too large to enable the use ofthe composition for the production of a silicon wafer carrier.

EFFECT OF THE INVENTION

This invention provides a silicon wafer carrier having high mechanicalproperties and heat-resistance as well as low generation of volatile gasand elution of metals suppressed to an extent not to essentially causethe surface contamination of a silicon wafer.

This invention also provides a silicon wafer carrier having excellentpermanent antistaticity as well as low generation of volatile gas andelution of metals suppressed to an extent not to essentially cause thesurface contamination of a silicon wafer.

What is claimed is:
 1. A silicon wafer carrier which comprises: (a) 100parts by weight of a polyester, (b) 5 to 100 parts by weight of apolyether ester amide, (c) 10 to 2,500 ppm (based on the polyether esteramide) of an alkaline metal and (d) 0 to 40 parts by weight of amodified polyolefin, generating not more than 10 ppm of volatile gas bythe heat-treatment at 150° C. for 60 minutes, and eluting not more than10 ppm of the alkaline metal by the immersion in pure water at 80° C.for 120 minutes.
 2. A silicon wafer carrier which comprises: (a) 100parts by weight of a polyester, (b) 5 to 30 parts by weight of apolyether ester amide and (c) 10 to 2,500 ppm (based on the polyetherester amide) of an alkaline metal, containing a polyether ester amidephase having an aspect ratio of 3 or more, a minor diameter of 1 μm orless and a major diameter of 1 μm or more in a polyester phase in therange from the surface of the silicon wafer carrier to the depth of 20μm, generating not more than 10 ppm of volatile gas by theheat-treatment at 150° C. for 60 minutes, and eluting not more than 10ppm of the alkaline metal by the immersion in pure water at 80° C. for120 minutes.
 3. A silicon wafer carrier which comprises: (a) 100 partsby weight of a polyether ester, (b) 31 to 100 parts by weight of apolyether ester amide, (c) 10 to 2,500 ppm (based on the polyether esteramide) of an alkaline metal and (d) 1 to 40 parts by weight of amodified polyolefin, containing a polyether ester amide phase having anaspect ratio of 3 or more, a minor diameter of 1 μm or less and a majordiameter of 1 μm or more in a polyester phase in the range from thesurface of the silicon wafer carrier to the depth of 20 μm, generatingnot more than 10 ppm of volatile gas by the heat-treatment at 150° C.for 60 minutes, and eluting not more than 10 ppm of the alkaline metalby the immersion in pure water at 80° C. for 120 minutes.
 4. A siliconwafer carrier which comprises: (a) 100 parts by weight of a polyester,(b) 5 to 100 parts by weight of a polyether ester amide, (c) 10 to 2,500ppm (based on the polyether ester amide) of an alkaline metal and (d) 0to 40 parts by weight of a modified polyolefin, generating not more than10 ppm of volatile gas by the heat-treatment at 150° C. for 60 minutes,and eluting not more than 10 ppm of the alkaline metal by the immersionin pure water at 80° C. for 120 minutes, wherein the modified polyolefinhas, on its terminal or side group, a functional group reactive with anester or amide group.
 5. A silicon wafer carrier which comprises: (a)100 parts by weight of a polyester, (b) 5 to 100 parts by weight of apolyether ester amide, (c) 10 to 2,500 ppm (based on the polyether esteramide) of an alkaline metal and (d) 0 to 40 parts by weight of amodified polyolefin, generating not more than 10 ppm of volatile gas bythe heat-treatment at 150° C. for 60 minutes, and eluting not more than10 ppm of the alkaline metal by the immersion in pure water at 80° C.for 120 minutes, wherein the polyester (a) has an intrinsic viscosity of0.6 to 1.2, the polyether ester amide (b) has a melt viscosity of 10 to1,000 Pa.S at 260° C. and a shearing rate of 1,000 sec⁻¹, and the meltviscosity ratio of the polyether ester amide to the polyester is between0.01 and 1 under the above condition.
 6. A process for producing asilicon wafer carrier which comprises: (a) 100 parts by weight of apolyester, (b) 5 to 100 parts by weight of a polyether ester amide, (c)10 to 2,500 ppm (based on the polyether ester amide) of an alkalinemetal and (d) 0 to 40 parts by weight of a modified polyolefin,generating not more than 10 ppm of volatile gas by the heat-treatment at150° C. for 60 minutes, and eluting not more than 10 ppm of the alkalinemetal by the immersion in pure water at 80° C. for 120 minutes, theprocess being characterized by molding a polyester (a) having anintrinsic viscosity of from 0.6 to 1.2 and a polyether ester amide (b)having a melt viscosity of 10 to 1,000 Pa.S measured at 260° C. and ashear rate of 1,000 sec⁻¹ while keeping the melt viscosity ratio of thepolyether ester amide (b) to the polyester (a) between 0.01 and
 1. 7. Asilicon wafer carrier which comprises: (a) 100 parts by weight of apolyether ester, (b) 31 to 100 parts by weight of a polyether esteramide, (c) 10 to 2,500 ppm (based on the polyether ester amide) of analkaline metal and (d) 1 to 40 parts by weight of a modified polyolefin,containing a polyether ester amide phase having an aspect ratio of 3 ormore, a minor diameter of 1 μm or less and a major diameter of 1 μm ormore in a polyester phase in the range from the surface of the siliconwafer carrier to the depth of 20 μm, generating not more than 10 ppm ofvolatile gas by the heat-treatment at 150° C. for 60 minutes, andeluting not more than 10 ppm of the alkaline metal by the immersion inpure water at 80° C. for 120 minutes, wherein the modified polyolefinhas, on its terminal or side group, a functional group reactive with anester or amide group.